This invention relates to gear shaping machines and more particularly to a gear shaping machine in which the helical advancement of teeth being cut in a gear blank can be changed without removing and replacing cutter guides.
In prior art gear shaping machines, a blank is mounted on a work table which is adapted to rotate the blank at a desired rate of speed about its central axis. The rotation of the blank is synchronized with the rotation of a cutting tool. The gear is generated by the congugate action of the blank rolling together with the cutting tool whose teeth are in the form of a mating gear for the gear being cut. In such prior art machines, the blank remains axially stationary during the shaping process while the cutting tool is reciprocated axially relative to the blank thereby cutting or shaping the teeth desired into the surface of the blank. The cutter makes a series of cutting strokes in the surface of the blank as the cutter and blank rotate in synchronism. Simultaneously, the cutter may be advanced radially relative to longitudinal axis of the blank to the depth of the teeth desired.
The longitudinal extent of the cutting tool stroke is controlled by an axially reciprocating spindle. In prior art type of machine, this is accomplished by coupling the spindle to an adjustable eccentric mounted on a drive shaft or by a hydraulic piston. The distance of the eccentric from the drive shaft axis determines the extent that the spindle is reciprocated. By adjusting the degree of eccentricity the machine operator can selectively increase or decrease the stroke length as required by the thickness of the blank being shaped.
As the cutter spindle is reciprocated axially it is also rotated in synchronism with the gear blank. This rotational movement may be provided, for example, by a worm driven worm gear which remains axially fixed while the spindle reciprocates. The coupling between the worm gear and the spindle simulates a sliding key or spline to allow axial movement of the spindle while it is being rotated. This coupling is referred to as a guide. In prior art machines; the inner portion of the guide is fixed to the spindle and is named the spindle portion and the outer portion of the guide is fixed to the worm gear and is named the worm gear portion. The guide also acts to establish the helix angle, if any, of the gear being cut. For example, if the helix angle of the work piece is to be zero degrees, the mating surfaces of the guide extend in the axial direction. On the other hand, if the helix angle of the work piece is to be greater than zero degrees, the mating surfaces of the guide have an appropriate helix angle, or finite lead, causing the reciprocating axial movement of the spindle to produce a corresponding helical motion of the cutter teeth. The pitch or lead of the guide must be such that the cutter teeth follow the helix of the gear. A single helical guide may be used to cut different gears having different helix angles by varying the outside diameter of the cutter. However, this helical range is limited by cutter diameter limitations.
In prior art machines, a number of guides were used, each having a different helix angle ranging from zero to some large finite value. Each time a change in the helix angle was required, it was necessary for the machine operator to shut down the machine and replace the guide.